US2513187A - Silver cleaner - Google Patents

Description

Patented June 27, 1950 UNITED STAT,

SILVER CLEANER Harry Linkletter, Englewood, N. J and William Van Kirk, Richmond Hill, N. Y., assignors, by mesne assignments, to Ultra Chemical Works, Inc., Paterson, N. J., a corporation of New Jersey N 0 Drawing. I Application March 26, 1947,

. f Serial N0. 737,402

This invention relates to the art of electrolytic silver cleaning and is specifically directed toan improved composition for use for such purpose.

It has long beenknown that the tarnish on silverware can be effectively removed by placing the silverware in an aqueous solution of an electrolyte in contact with a metal anodic thereto. An electrolytic cell is thereby set up, and the tarnish, which consists largely of silver sulfide, is

reduced to metallic silver with evolution of hydr'ogen sulfide while a corresponding portion of the anodic metal is oxidized. Aluminum is generally utilized as the anodic metal although other metals anodic to silver can be used in its place.

Various water-soluble alkali metal and alkaline earth metal compounds such as sodium hydroxide, trisodium phosphate, sodium carbonate, and the like have been proposed as the electrolyte. Of such compounds sodium hydroxide is by far the most effective since it possesses an extremely high pH, a characteristic essential for rapid and efiicient detarnishing especially at hot tap water (140 to 160 F.) and lower temperatures. Sodium hydroxide is impracticable for household use, however, because of the danger and difliculty involved in handling it either in a concentrated solution or dry.

We have now discovered that this disadvantage can be effectively eliminated by using as the electrolyte a mixture of calcium hydroxide and sodium bicarbonate. When such mixture is placed in water, these two compounds react to form sodium hydroxide; and these compounds can be so proportioned that the resulting alkaline solution has a pH closely approximatingthat of an equivalent amount of sodium hydroxide.

Advantageously, the calcium hydroxide and the sodium bicarbonate are admixed in proportions within the range of 40 to 60 parts by weight of the former to 60 to 40 parts by weight of the latter. Within this range the most effective and the optimum detarnishing action is obtained. Mixtures of these two compounds containing a greater amount of calcium hydroxide produce solutions that are not nearly so efiicient detarnishing mediums; and mixtures containing a greater amount of sodium bicarbonate produce solutions having a pH too low for satisfactory cleaning of silver at hot tap water and lower temperatures. The maximum pH (12.5-13.0) of the present silver-cleaning bath is attained when the present electrolyte contains the calcium hydroxide and the sodium bicarbonate in approximately equal proportions by weight.

2 Claims. (Cl. 204144) in powdered form in a heat-sealed aluminum foil envelope, in amanner such asthat described in the copending application of Harry Linkletter and George Welp, S. N. 602,166, filed June 28, 1945, (now abandoned) to provide a unitary silver cleaner package. As disclosed in the copending application f Harry Linkletter, S. N. 602,167, filed June 28, 1945, (now abandoned a surfaceactive agent such as the sodium salt of suli'onated mineral oil and-thelike can with advantage be incorporated in the present electrolyte in order to cut any oil or grease present on the silverware to be cleaned and to reduce the time required for the desired cleaning to be efi'ected.

The following formulation represents a typical example of the present improved electrolyte:

Weight per cent Calcium hydroxide household'use can be prepared by sealing 28 gm. of this composition, advantageously in powdered form, in an'envelope made from a 32-square inch aluminum foil of suflicient thickness (advantageously not less than 0.0015 inch) to withstand the deteriorating efiect of the electrolytic oxidation.

Addition of such an amountoi this composition to 3 quarts of water produces approximately a 1% solution having a pH of about 12.6. Although the resulting solution has a very high pH, it is not harmful to the hands because of its very low concentration of caustic. The dry electrolyte itself can be handled with complete safety and without difiiculty before it is added to the water. Obviously, more or less water (for example, 4 to 2 quarts) can be used to make up the detarnishing solution, in which case the concentration of the caustic is respectively somewhat less or somewhat greater.

Normally tarnished articles can be cleaned with the present electrolyte in 10 seconds or less and heavily tarnished silverware in 1 to 5 minutes, depending on the severity of the tarnish. The present composition effectively cleans tarnished silver over a wide range of temperature, from cold tap water temperatures to the boiling point of water. For example, excellent detarnishing of silverware was obtained with Our electrolyte can be conveniently packaged aqueous solutions of the .above specific composition maintained at 120 F., 160 F., and 205 to 210 F.

The hydrogen sulfide which is formed by the electrolytic reduction of the silver sulfide tarnish dissolves to some extent in alkaline electrolytes. The accumulation of this hydrogen sulfide after many articles have been detarnished tends to decrease the cleaning efiiciency of the solution as evidenced by the formation of a tarnish cast on the silverware being cleaned. This poisoning action is hastened as the operating temperature of the detarnishing bath is lowered because of the greater solubility of hydrogen sulfidev in cold solutions. Our electrolyte, however, was found to have a longer effective life than other electrolytes employed in common practice. We believe that this effect may be the result of a chemical combination of the excess calcium hydroxide with a portion of the accumulating hydrogen sulfide. to form an insoluble sulfide, which, although unstable, tends to delay the poisoning action.

We have found that the inclusion of a small percentage of potassium chlorate in the present electrolyte acts as an accelerater of the detarnishing action particularly at cold temperatures. Advantageously, about 2.4 to of potassium chlorate based on the weight of the entire electrolyte is utilized for this purpose; and best results appear to be obtained with an amount of potassium chlorate on the order of 2.5%. No practical effect is obtained with proportions of potassium chlorate less than 2.4%, while proportions above 5% retard the detarnishing action of the electrolyte. v

The following formulation is typical of our potassium chlorate-containing electrolyte:

Weight per cent Calcium hydroxide 56.0 Sodium bicarbonate 41.0

Potassium chlorate 2.5 Sodium salt of sulfonated mineral oil 0.5

Other compounds that are commonly employed potassium permanganate, potassium dichromate,

calcium hypochlorite, zinc sulfate, copper oxide, and mercuric sulfate are of no value for this purpose.

Solutions of calcium hydroxide, while possessing a pH of 11.4, do not produce optimum cleaning efllciency at low temperatures. Solutions of sodium bicarbonate, on the other hand, while possessing a pH of only 8.1, effectively detarnish silverwear at the boiling temperature; but below this temperature the time required for detarnishing' is substantially increased, and the tarnish is not effectively removed. Moreover, heavily tarnished silverware is not efficiently cleaned with sodium bicarbonate as the electrolyte.

We claim:

1. A dry composition for silver-cleaning comprising. aluminum metal and an electrolyte consisting of a mixture of approximately 40 to parts by weight of calcium hydroxide, 60 to 40 parts by weight of sodium bicarbonate, and 2.4 to 5% of potassium chlorate based on the weight of the entire electrolyte.

2. A dry composition for silver-cleaning comprising aluminum metal and an electrolyte consisting of a mixture of approximately equal parts by weight of calcium hydroxide and sodium bicarbonate and 2.5% of potassium chlorate based on the weight of the entire electrolyte.

HARRY. LINKLETTER. WILLIAM VAN KIRK.

REFERENCES. CITED The following references are of record in th file of this patent:

UNITED STATES PATENTS Number Name Date 1,049,603 Rosenberg Jan. 7, 1913 FOREIGN PATENTS Number Country Date 14,485 Great Britain of 1884 23,329 Great Britain of 1897 15,962 Great Britain of 1908 5,684 Great Britain of 1911 OTHER REFERENCES A. P. 'Cz publication, 385,561,May 11, 1943.

Claims (1)

1. A DRY COMPOSITION FOR SILVER-CLEANING COMPRISING ALUMINUM METAL AND AN ELECTROLYTE CONSISTING OF A MIXTURE OF APPROXIMATELY 40 TO 60 PARTS BY WEIGHT OF CALCIUM HYDROXIDE, 60 TO 40 PARTS BY WEIGHT OF SODIUM BICARBONATE, AND 2.4 TO 5% OF POTASSIUM CHLORATE BASED ON THE WEIGHT OF THE ENTIRE ELECTROLYTE.